You can choose a custom icon for any file or folder using your own pictures, icons downloaded from the web, or the icon from another file or folder.
On your Mac, select the file or folder whose icon you want to use, then choose File > Get Info.
At the top of the Info window, click the icon, then choose Edit > Copy.
Select the other file or folder, then choose File > Get Info.
Click the icon at the top of the Info window.
The folder icon is replaced with the picture you chose.
If Edit > Paste isn’t available, make sure you click the icon at the top of the Info window.
After you paste, if you see a generic JPEG or PNG image instead of your own picture, make sure you click the icon in the Info window before choosing Edit > Copy.
-"Change icons for files or folders on Mac"